Proteomics has special significance for Xenopus research because key events in meiosis, fertilization and early development are regulated at the level of translation, post- translational modification and proteolysis, and not by transcription. Proteomics is the only tool for systematically investigating these levels of regulation and discovering new mechanisms. We propose to develop a cutting edge proteomic research platform for Xenopus embryos and egg extract by migrating technology developed in human and yeast systems, and to publicly disseminate the databases and tools we develop. We will also optimize methods for proteomic analysis of protein complexes and compartments in egg extract. Using these tools we will quantify relative amounts of >5,000 proteins, >10,000 phosphorylation sites and >1,500 ubiquitination sites in early development and in egg extracts under normal and perturbed conditions. We will investigate the mechanism of cell cycle regulation, how the cell cycle changes during early development, how microtubules are nucleated, and how embryos detect changes in the nucleus to cytoplasm ratio.